990 CLD Autoline™ Leak Detector
DR
AFT 2/2/04
4-21
Miscellaneous Problems
The LEAK RATE bar graph stays fully lit on all ranges under all conditions, regardless of the
state of test.
While, this condition may indicate a helium-swamped system, it can be caused by a blown
preamplifier, if the preamplifier cable is not connected to the spectrometer tube, or by a
wrong revision controller and cable assembly.
1. Check that the preamplifier cable is attached.
2. If the condition persists and you are sure that it is not helium swamping (which clears up
quickly) and the controller has not been recently replaced, then turn off the leak
detector, unplug the preamplifier from the spectrometer tube, and plug it into either a
known good spectrometer tube or a known good preamplifier.
3. Install the known good preamplifier in the spectrometer tube to run this test. The
spectrometer tube need not be evacuated for this test. Be sure to handle the preamplifier
assembly very carefully and observe proper static-sensitive component handling
procedures.
4. Turn on the leak detector.
After the initial lamp test (a few seconds), the bar graph should not be on in all ranges.
However, there may be a significant up-scale reading and this is normal.
❑
If the bar graph acts normally, then the problem is a blown preamplifier. Follow
the procedures in the instruction manual for removal and replacement of the
preamplifier assembly.
❑
If the problem persists, then the controller may be the wrong revision for the cable
in the system or the controller may be defective. Perform 990 Controller cable
tests for a shorted cable.
5. Check that the spectrometer tube cables are properly connected, then remove the cable
clamping plates (retainers).
6. Measure the DC voltage between the cable clamp on the ion source and preamplifier to
the spectrometer tube ground stud. If the voltage is greater than 1 V, the cable is shorted
to the clamp. Replace it and continue the diagnostics. If there is no short in the cable
assembly, turn off the leak detector MAIN POWER switch, then remove the connector
from the ion source and preamplifier.
7. Turn on the MAIN POWER switch then re-measure the ion, repeller, and focus voltages
on the leak detector front panel. If they are:
❑
Correct, turn off the MAIN POWER switch, plug in the preamplifier and
re-measure the voltages. If they are still correct, replace the ion source.
❑
Not correct, replace the preamplifier, it has developed a short.
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